// Copyright 2010 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// The routines exported by this module are subtle.  If you use them, even if
// you get the code right, it will depend on careful reasoning about atomicity
// and memory ordering; it will be less readable, and harder to maintain.  If
// you plan to use these routines, you should have a good reason, such as solid
// evidence that performance would otherwise suffer, or there being no
// alternative.  You should assume only properties explicitly guaranteed by the
// specifications in this file.  You are almost certainly _not_ writing code
// just for the x86; if you assume x86 semantics, x86 hardware bugs and
// implementations on other archtectures will cause your code to break.  If you
// do not know what you are doing, avoid these routines, and use a Mutex.
//
// It is incorrect to make direct assignments to/from an atomic variable.
// You should use one of the Load or Store routines.  The Relaxed  versions
// are provided when no fences are needed:
//   Relaxed_Store()
//   Relaxed_Load()
// Although there are currently no compiler enforcement, you are encouraged
// to use these.
//

#ifndef V8_BASE_ATOMICOPS_H_
#define V8_BASE_ATOMICOPS_H_

#include <stdint.h>

// Small C++ header which defines implementation specific macros used to
// identify the STL implementation.
// - libc++: captures __config for _LIBCPP_VERSION
// - libstdc++: captures bits/c++config.h for __GLIBCXX__
#include <cstddef>

#include "src/base/base-export.h"
#include "src/base/build_config.h"

namespace v8 {
namespace base {

    using Atomic8 = char;
    using Atomic16 = int16_t;
    using Atomic32 = int32_t;
#if defined(V8_HOST_ARCH_64_BIT)
// We need to be able to go between Atomic64 and AtomicWord implicitly.  This
// means Atomic64 and AtomicWord should be the same type on 64-bit.
#if defined(__ILP32__)
    using Atomic64 = int64_t;
#else
    using Atomic64 = intptr_t;
#endif // defined(__ILP32__)
#endif // defined(V8_HOST_ARCH_64_BIT)

    // Use AtomicWord for a machine-sized pointer.  It will use the Atomic32 or
    // Atomic64 routines below, depending on your architecture.
    using AtomicWord = intptr_t;

    // Atomically execute:
    //      result = *ptr;
    //      if (*ptr == old_value)
    //        *ptr = new_value;
    //      return result;
    //
    // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value".
    // Always return the old value of "*ptr"
    //
    // This routine implies no memory barriers.
    Atomic16 Relaxed_CompareAndSwap(volatile Atomic16* ptr, Atomic16 old_value,
        Atomic16 new_value);
    Atomic32 Relaxed_CompareAndSwap(volatile Atomic32* ptr, Atomic32 old_value,
        Atomic32 new_value);

    // Atomically store new_value into *ptr, returning the previous value held in
    // *ptr.  This routine implies no memory barriers.
    Atomic32 Relaxed_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value);

    // Atomically increment *ptr by "increment".  Returns the new value of
    // *ptr with the increment applied.  This routine implies no memory barriers.
    Atomic32 Relaxed_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment);

    Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
        Atomic32 increment);

    // These following lower-level operations are typically useful only to people
    // implementing higher-level synchronization operations like spinlocks,
    // mutexes, and condition-variables.  They combine CompareAndSwap(), a load,
    // or a store with appropriate memory-ordering instructions.  "Acquire"
    // operations ensure that no later memory access can be reordered ahead of the
    // operation. "Release" operations ensure that no previous memory access can
    // be reordered after the operation.  "Fence" operations have both "Acquire"
    // and "Release" semantics. A SeqCst_MemoryFence() has "Fence" semantics, but
    // does no memory access.
    Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
        Atomic32 old_value,
        Atomic32 new_value);
    Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
        Atomic32 old_value,
        Atomic32 new_value);

    void SeqCst_MemoryFence();
    void Relaxed_Store(volatile Atomic8* ptr, Atomic8 value);
    void Relaxed_Store(volatile Atomic16* ptr, Atomic16 value);
    void Relaxed_Store(volatile Atomic32* ptr, Atomic32 value);
    void Release_Store(volatile Atomic32* ptr, Atomic32 value);

    Atomic8 Relaxed_Load(volatile const Atomic8* ptr);
    Atomic16 Relaxed_Load(volatile const Atomic16* ptr);
    Atomic32 Relaxed_Load(volatile const Atomic32* ptr);
    Atomic32 Acquire_Load(volatile const Atomic32* ptr);

// 64-bit atomic operations (only available on 64-bit processors).
#ifdef V8_HOST_ARCH_64_BIT
    Atomic64 Relaxed_CompareAndSwap(volatile Atomic64* ptr, Atomic64 old_value,
        Atomic64 new_value);
    Atomic64 Relaxed_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value);
    Atomic64 Relaxed_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
    Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);

    Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
        Atomic64 old_value,
        Atomic64 new_value);
    Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
        Atomic64 old_value,
        Atomic64 new_value);
    void Relaxed_Store(volatile Atomic64* ptr, Atomic64 value);
    void Release_Store(volatile Atomic64* ptr, Atomic64 value);
    Atomic64 Relaxed_Load(volatile const Atomic64* ptr);
    Atomic64 Acquire_Load(volatile const Atomic64* ptr);
#endif // V8_HOST_ARCH_64_BIT

} // namespace base
} // namespace v8

#if defined(V8_OS_WIN)
#include "src/base/atomicops_internals_std.h"
#else
// TODO(ulan): Switch to std version after performance regression with Wheezy
// sysroot is no longer relevant. Debian Wheezy LTS ends on 31st of May 2018.
#include "src/base/atomicops_internals_portable.h"
#endif

// On some platforms we need additional declarations to make
// AtomicWord compatible with our other Atomic* types.
#if defined(V8_OS_MACOSX) || defined(V8_OS_OPENBSD) || defined(V8_OS_AIX)
#include "src/base/atomicops_internals_atomicword_compat.h"
#endif

#endif // V8_BASE_ATOMICOPS_H_
